This application is related to the Applicant""s co-pending application Ser. No. 09/254,391, filed Mar. 8, 1999.
The invention relates to a data bus for communication among several devices in a motor vehicle which serve to ensure the safety of the passengers.
Such safety devices include actuators (such as airbags and safety belt tighteners, for example); or they also may be sensors that provide information regarding safety conditions or test data, respectively. Such a data bus differs significantly from other known, common place data buses in vehicles, both in terms of its importance and functionality. Known data buses serve to exchange data between all components. The components are assigned to subsystems of the vehicle, and include, for example, digital engine electronics, electronic hydraulic transmission control and an anti-lock braking system. Such subsystems work satisfactorily only when data exchange among all components is made possible.
In contrast, in a data bus for safety-relevant devices, the exchange of data among all components is not the primary goal. Instead, the capability to be able to react as fast as possible to critical situations is of primary importance. Here, the term xe2x80x9creactxe2x80x9d means the deployment of an air bag, for example, in the area of the door. If the possibility for all components of such a data bus to communicate with each other is desired, then this would result in critical situations, and as a consequence (because of the execution times of the signals of all components) the information concerning the critical safety condition does not arrive at the appropriate actuator in time.
It is therefore an object of the invention to create a data bus which is suitable for interconnecting devices which ensure the safety of passengers in a vehicle.
Another object of the invention is to provide a data bus in which transmission of a signal to the appropriate actuator in a timely manner is guaranteed.
These and other objects and advantages are achieved by the data bus according to the invention, in which the components of the data bus are synchronized via a synchronizing pulse, the phase of the basic cycle of the synchronizing pulse is smaller than the cumulative transmission time of all of the components, and the phase of the basic cycle equals the cumulative transmission times of a predetermined number of the components with the highest priority, plus the time intervals (t_wx) which separate such transmissions from each other and from the synchronizing pulses.
The use of a synchronizing pulse serves to determine the renewal rate of the data, and to keep it constant independently of the number of components. The choice of the basic cycle phase in the manner described serves when needed (i.e., in a situation which is critical for ensuring the safety of the passengers) to release one or more actuators, such that only the components which are responsible for reacting to this particular condition are allowed to transmit their signal. These components of the data bus are usually those with the highest transmission priority. After the output of the synchronizing pulse, they access the data bus and make available the information regarding a condition which is critical for the safety of the passengers. The components which react to this information, for example, by deploying an airbag, cannot themselves access the data bus during the basic cycle phase (a condition which also applies for those components that send data with a lower priority ranking).
The basic cycle phase is timed such that the components having the highest priority can transmit to the data bus during the basic cycle phase (even when all of them signal a critical condition), while components having a lower priority ranking cannot access the data bus in these cases. As long as the condition which is critical for ensuring the safety of the passengers lasts, and the components with the highest priority output transmit their data to the data bus, other components are practically prevented from transferring their information to the data bus.
International patent document WO 96/08097 A discloses a process for the transfer of data between data processing stations or devices for automation technology, in which all stations work according to a constant, synchronized time cycle. The cycle is divided into three phases which run in the following order: synchronizing phase, broadcast phase and message phase. In the broadcast phase, each station releases exactly one segment of data for transmission (which is actually transmitted), while during the message phase each station may release and transmit (when authorized to do so) until the message phase comes to an end.
In accordance with the objects of the invention, the basic cycle phase has been significantly minimized. Therefore, a component may access the data bus at a point in time when the next synchronizing pulse is being sent. In this case, it is desirable to delay the output of the synchronizing pulse until the component has completed its transmission.
Particularly in a case such as this, in order to be able to maintain the phase frequency, output of the following synchronizing pulse is to be synchronized with the next to last previous synchronizing pulse. If the next to last previous synchronizing pulse is designated as the first pulse and the following as the second pulse, third pulse, etc., then the time span between the first and the second pulses is larger than the phase of the basic cycle, while the time span between the second and the third pulses is smaller than the phase of the basic cycle. Should a component once more transmit to the data bus at the output time of the third synchronizing pulse, then the third synchronizing pulse is also output with a delay. The subsequent synchronizing pulse, (in this case the fourth one), compensates for exceeding the time provided, etc.
The data bus can be a conventionally hard-wired system. For protection from interference, it can be advantageous to provide a data bus which is based on beam wave guides with active star couplers connecting the components to the data bus.
With regard to the configuration and the response characteristic of the data bus, it can be advantageous if the components transmit only in a situation which is critical for ensuring the safety of the passengers. In addition, the components can also transmit in greater time intervals (a multiple of the basic cycle phase). In this way, it is guaranteed that in situations which are not critical for ensuring the safety of the passengers, the information of those components which do not have the highest transmission priority in a situation which is critical for safety reasons, is transmitted to the data bus.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.